Data storage device demodulating servo stripes using matched filter

ABSTRACT

A data storage device is disclosed comprising at least one head configured to access a magnetic tape comprising a plurality of servo frames each comprising an A servo burst, a B servo burst, a C servo burst, and a D servo burst. The A servo burst in a first servo frame is read using the head to generate a first read signal which is sampled to generate first signal samples. A first matched filter matched to the A servo burst filters the first signal samples to generate first filtered samples within a first burst window, and the first burst window is updated based on the first filtered samples. The first filtered samples within the first burst window are processed to generate a position error signal (PES), and a position of the head is controlled relative to the magnetic tape based on the PES.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. patent applicationSer. No. 17/176,024 filed on Feb. 15, 2021, which claims priority toU.S. Provisional Patent Application Ser. No. 63/086,153, filed on Oct.1, 2020, which are hereby incorporated by reference in their entirety.

BACKGROUND

Conventional tape drive storage systems comprise a magnetic tape woundaround a dual reel (reel-to-reel cartridge) or a single reel (endlesstape cartridge), wherein the reel(s) are rotated in order to move themagnetic tape over one or more transducer heads during write/readoperations. The format of the magnetic tape may be single track ormultiple tracks that are defined linearly, diagonally, or arcuate withrespect to the longitudinal dimension along the length of the tape. Witha linear track format, the heads may remain stationary relative to thelongitudinal dimension of the tape, but may be actuated in a lateraldimension across the width of the tape as the tape moves past the heads.With a diagonal or arcuate track format, the heads may be mounted on arotating drum such that during access operations both the heads and tapeare moved relative to one another (typically in opposite directionsalong the longitudinal dimension of the tape).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a data storage device according to an embodimentcomprising at least one head configured to access a magnetic tape.

FIG. 1B is a flow diagram according to an embodiment wherein digitaldata is demodulated based on a number of servo stripes in a servo frame.

FIGS. 1C and 1D show a servo frame wherein an A and B servo burstconsists of five servo stripes, and a C and D servo burst consists offour servo stripes when representing a digital “0” or three servostripes when representing a digital “1”.

FIG. 1E shows a data storage device comprising a cartridge assemblycomprising a magnetic tape, and a tape drive assembly configured toaccess the magnetic tape.

FIGS. 2A and 2B show a prior art servo frame wherein digital data isdemodulated from the C and D bursts based on a time shift of the servostripes.

FIGS. 3A and 3B show an embodiment wherein a format of the servo stripesin the A and B servo bursts matches a format of the servo stripes in theC and D servo bursts except for one or two missing servo stripesdepending on whether the servo stripes represent a digital “0” or “1”.

FIGS. 4A-4D show an embodiment wherein the missing servo stripes in theC and D servo bursts represent one of four digital values.

FIGS. 5A-5H show an embodiment wherein the missing servo stripes in theC and D servo bursts represent one of eight digital values.

FIGS. 6A and 6B show an embodiment wherein a position error signal (PES)is generated at a rate of two measurements per servo frame.

FIGS. 7A and 7B show an embodiment wherein a position error signal (PES)is generated at a rate of four measurements per servo frame.

FIGS. 8A and 8B show embodiments wherein a plurality of matched filtersmeasure an average timestamp for each servo burst.

FIG. 9A shows an embodiment wherein the output of an A/B matched filteris processed during a burst window that estimates a center of acorresponding A/B servo burst.

FIG. 9B shows an embodiment wherein the output of a C/D matched filteris processed during a burst window that estimates a center of acorresponding C/D servo burst.

FIG. 10A shows an embodiment wherein the output of the matched filter isinterpolated to increase the accuracy of the PES.

FIG. 10B shows an embodiment wherein the output of the matched filter isqualified before being interpolated.

FIG. 10C shows an embodiment wherein the qualifying criteria prior tothe interpolation comprises a burst window that estimates a center of aservo burst.

FIG. 10D shows an embodiment wherein the qualifying criteria prior tothe interpolation comprises a burst window followed by a coarse peakdetector.

FIG. 11 shows an example wherein interpolating the output of the matchedfilter increases the accuracy of the average timestamp for generatingthe PES.

DETAILED DESCRIPTION

FIGS. 1A and 1B show a data storage device according to an embodimentcomprising at least one head 2 configured to access a magnetic tape 4comprising a plurality of servo frames each comprising a plurality ofservo stripes (e.g., FIG. 1C or 1D). The data storage device furthercomprises control circuitry 6 configured to execute the flow diagram ofFIG. 1B, wherein the servo stripes are read using the head to generate aread signal which is processed to detect a position error signal (PES)used to control a position of the head relative to the magnetic tape(block 8). The read signal is also demodulated into digital data basedon a number of servo stripes detected in each servo frame (block 10).

In the embodiment of FIG. 1A, the data storage device comprises anembedded magnetic tape 4 installed into a tape drive assembly which, inone embodiment, may be the same form factor as a conventional diskdrive. In another embodiment shown in FIG. 1E, the magnetic tape 4 maybe housed in a cartridge assembly 3 that is inserted into (and ejectedfrom) a tape drive assembly 5 similar to a conventional tape drivemanufactured under the Linear Tape-Open (LTO) standard. In oneembodiment, the tape drive assembly 5 comprises the head 2 configured toaccess the magnetic tape 4, and the control circuitry 6 configured toexecute the flow diagram of FIG. 1B.

FIGS. 1C and 1D show an example servo frame according to an embodimentwherein a first subframe comprises A and B servo bursts each consistingof five servo stripes, and a second subframe comprises C and D servobursts each consisting of four servo stripes when representing a digital“0” or three servo stripes when representing a digital “1”. Any suitabledigital data may be encoded into the servo frames, such as alongitudinal position of the head along the length of the magnetic tape.In the example embodiment of FIGS. 1C and 1D, a single bit of thedigital data is encoded into each servo frame, whereas in otherembodiments described in greater detail below, multiple bits may beencoded into each servo frame. In one embodiment, the differing numberof servo stripes between the sub-frames may also be used to distinguishbetween the subframes. That is, in one embodiment the A and B servobursts of the first subframe may be considered a “sync” subframe whichis distinguished from the second subframe due to having five servostripes per servo burst as compared to four or three servo stripes perservo burst. Each servo stripe may be written to the magnetic tape inany suitable manner, wherein in one embodiment each servo stripe may bewritten as an isolated dibit using a suitable write head.

In one embodiment, the PES for controlling the lateral position of thehead relative to the width of the magnetic tape is generated based on aratio of time intervals detected between the servo stripes. For example,a first time interval may be measured between a servo stripe in the Aservo burst and a corresponding servo stripe in the B servo burst, and asecond time interval may be measured between the servo stripe in the Aservo burst and a corresponding servo stripe in the C servo burst. ThePES may then be generated as the ratio of the first and second timeintervals, wherein the ratio is independent of the speed of the magnetictape. In one embodiment, multiple time intervals may be measured formultiple of the servo stripes, wherein the resulting ratios may beaveraged in order to generate the PES in a manner that attenuates noisethat may otherwise obfuscate a single ratio measurement. In anotherembodiment described below, an average timestamp may be generated foreach servo burst and the time intervals measured based on the averagetimestamps in order to attenuate noise in the PES measurement.

FIGS. 2A and 2B show a prior art format of a {5,4} servo frame meaningthe first subframe of A and B servo bursts consist of five servostripes, and the second subframe of C and D servo bursts consist of fourservo stripes. A digital “0” or “1” is encoded into the second subframebased on time shifting the servo stripes. That is, in FIG. 2A a “0” isencoded into the second subframe by recording the servo stripes withouta time shift, and in FIG. 2B a “1” is encoded into the second subframeby recording the third and fourth servo stripes with a time shiftrelative to the first and second servo stripes.

FIGS. 3A and 3B show an embodiment wherein a digital value is encoded byvarying the number of servo stripes written to the C and D servo bursts.In FIG. 3A a “0” is encoded by writing a {5,4} servo frame, and in FIG.3B a “1” is encoded by writing a {5,3} servo frame. In this embodiment,a format of the servo stripes in the first subframe of A and B servobursts matches a format of the servo stripes in the second subframe of Cand D servo bursts except for a single missing servo stripe (the middleservo stripe) when encoding a “0” as shown in FIG. 3A. A format of theservo stripes in the first subframe of A and B servo bursts matches aformat of the servo stripes in the second subframe of C and D servobursts except for two missing servo stripes (the second and fourth servostripes) when encoding a “1” as shown in FIG. 3B. Accordingly in thisembodiment, when measuring the PES time intervals between the servostripes within a subframe as well as between the subframes the pairingof the servo stripes remains constant. Alternatively when measuring anaverage timestamp for each servo burst, one or more missing servo stripswithin a servo burst does not change the average timestamp measurement.Also in this embodiment, the spacing of the servo stripes (including themissing servo stripes) in the first and second subframes remainsconstant such that the width of the first and second subframes aresubstantially equal, thereby simplifying the demodulation of the servoframes regardless as to the direction of tape movement (forward orbackward).

FIGS. 4A-4D show an embodiment wherein the second subframe encodes oneof four digital values (i.e., the second subframe encodes two bits ofdata). In FIG. 4A a “0” is encoded by writing a {7,6} servo frame withthe fourth servo stripe missing in the second subframe. In FIG. 4B a “1”is encoded by writing a {7,5} servo frame with the third and fifth servostripe missing in the second subframe. In FIG. 4C a “2” is encoded bywriting a {7,4} servo frame with the second, fourth, and sixth servostripes missing in the second subframe. In FIG. 4D a “3” is encoded bywriting a {7,5} servo frame with the second and sixth servo stripesmissing from the second subframe.

FIGS. 5A-5H show an embodiment wherein the second subframe encodes oneof eight digital values (i.e., the second subframe encodes three bits ofdata) by writing various permutations of a {9,N} servo frame. That is,nine servo stripes are written in the first subframe, and N=8, 7, 6 or 5servo stripes are written in the second subframe depending on thedigital value encoded into the second subframe as shown in FIGS. 5A-5H.

FIGS. 6A and 6B show an embodiment wherein a PES for controlling thelateral position of the head is generated at a rate of two measurementsper servo frame. In this embodiment, an average timestamp generated foreach servo burst is used to measure an average time interval between theservo bursts. The PES is then generated based on the ratio of selectedintervals as shown in FIGS. 6A and 6B in a manner that is independent oftape speed. FIGS. 7A and 7B show a similar embodiment wherein a PES forcontrolling the lateral position of the head is generated at a rate offour measurements per servo frame.

FIG. 8A shows an embodiment wherein a plurality of matched filters eachmatched to the servo stripes of a servo burst generates the averagetimestamp in order to generate the PES in the embodiments describedabove. In addition, the output of the matched filters matched to the C/Dservo bursts are also used to demodulate the digital value(s) encodedinto the C/D servo bursts. In the example of FIG. 8A, the servo frameformat is {7,6} when encoding a digital “0” value or {7,5} when encodinga digital “1” value. A first matched filter 12 correlates the readsignal with an expected series of pulses matching the servo stripes ofthe NB bursts, a second matched filter 14 correlates the read signalwith an expected series of pulses matching the servo stripes of the C/Dbursts encoding a “0” digital value, and a third matched filter 16correlates the read signal with an expected series of pulses matchingthe servo stripes of the C/D bursts encoding a “1” digital value. In theembodiment of FIG. 8A, the output of each matched filter is compared toa threshold, and the time at which the output exceeds the thresholdbecomes the average timestamp for the corresponding servo burst. Thatis, the output of the matched filter that matches the servo burst beingread will exceed the threshold due to the correlation exceeding thethreshold. In addition, when the output of the matched filter matched tothe C/D servo burst exceeds the threshold, the corresponding digitalvalue is also demodulated as shown in FIG. 8A.

FIG. 8B shows an embodiment wherein the outputs of the matched filtersare compared to one another to facilitate generating the timestamps anddemodulating the digital values. For example, in one embodiment atimestamp is generated (and a digital value demodulated) when theoutputs of each matched filter exceeds a gating threshold indicating thepulses in the read signal align with each of the matched filters (i.e.,the correlations reach a maximum). At this point, the matched filterhaving the highest output (highest correlation) corresponds to the servoburst being read and is therefore used to generate the timestamp as wellas demodulate the digital value.

In the embodiment of FIGS. 8A and 8B, the matched filters are shown asoperating in continuous time meaning the analog read signal iscorrelated with an analog filter having a continuous time impulseresponse substantially matched to the pulses generated by reading theservo stripes in each servo burst. In another embodiment, the matchedfilters may operate in discrete time meaning the analog signal issampled, and the signal samples filtered with a digital filter having adiscrete time impulse response substantially matched to the signalsamples of the pulses generated by reading the servo stripes in eachservo burst.

FIG. 9A shows an embodiment wherein the control circuitry 6 isconfigured to read the A servo burst in a first servo frame using thehead to generate a first read signal, sample the first read signal togenerate first signal samples, use a first matched filter matched to theA servo burst to generate first filtered samples in response to thefirst signal samples within a first burst window, first update the firstburst window based on the first filtered samples, process the firstfiltered samples to generate a position error signal (PES), and controla position of the head relative to the magnetic tape based on the PES.

In the embodiment of FIG. 9A, an A burst window and a B burst window areopened during an interval that estimates a center of the correspondingservo bursts so that the output of the NB matched filter 12 of FIG. 8Ais evaluated during the NB burst window, thereby improving the accuracyof the corresponding average timestamp. For example, in one embodimentthe output of the matched filter may be a periodic signal comprisingmultiple pulses with a center pulse representing the center of the servoburst. Evaluating the matched filter output during the burst windowhelps ensure the center pulse is the pulse that is detected (e.g., usingpeak detection) as opposed to mis-detecting a neighboring pulse. In theembodiment of FIG. 9A, an estimated time ta to the center of the next Aservo burst is computed as the measured A-A burst interval from theprevious servo frame (i-1) to the current servo frame (i). Acorresponding A burst window is then generated using any suitableplus/minus delta from the estimated time ta as shown in FIG. 9A. Asimilar B burst window is generated by computing an estimated time tbbased on the measured B-B burst interval from the previous servo frame(i-1) to the current servo frame (i) as shown in FIG. 9A. Each time theaverage timestamp is generated for the A servo burst or B servo burst,the corresponding A and B servo burst window for the next servo frame isupdated.

FIG. 9B shows an embodiment wherein a C burst window is generated forthe C servo burst and a D burst window is generated for the D servoburst. In this embodiment, the estimated time tc to the center of thenext C servo burst is generated as a fraction of the measured A-A burstinterval from the previous servo frame (i-1) to the current servo frame(i), wherein in this embodiment the predetermined fraction is thefraction of the A-A burst interval that is the A-C burst interval(AC/AA). Similarly in the embodiment of FIG. 9B, the estimated time tdto the center of the next D servo burst is generated as a fraction ofthe measured B-B burst interval from the previous servo frame (i-1) tothe current servo frame (i), wherein in this embodiment thepredetermined fraction is the fraction of the B-B burst interval that isthe B-D burst interval (BD/BB). Each time the average timestamp isgenerated for the A servo burst or B servo burst, the corresponding Cand D servo burst window for the next servo frame is updated.

FIG. 10A shows an embodiment wherein the control circuitry 6 isconfigured to read a first servo burst using the head to generate a readsignal 18 which is sampled 20 to generate signal samples 22. A firstmatched filter 24 matched to the first servo burst is used to filter thesignal samples 22 to generate filtered samples 26. At least part of thefiltered samples 26 are interpolated 28 to generate interpolated samples30, and the interpolated samples 30 are processed 32 to generate aposition error signal (PES) for controlling a position of the headrelative to the magnetic tape based on the PES.

In one embodiment, the output of the matched filter 24 represented bythe interpolated samples 30 may be a periodic signal comprising multiplepulses with a center pulse representing the center of the correspondingservo burst. In the embodiment of FIG. 10A, the control circuitry 6comprises a suitable peak detector 34 for detecting the peak of thecenter pulse which represents the average timestamp of the servo burstfor use in generating the PES as described above.

FIG. 10B shows an embodiment wherein the filtered samples 26 arequalified 36 based on a suitable qualifying criteria in order to selecta subset of the filtered samples 26 for further processing by theinterpolator 28. For example, in one embodiment the qualifying criteriamay comprise the filtered samples 26 exceeding a predetermined thresholdto ensure the amplitude of the filtered samples 26 is above a noisefloor. In an embodiment shown in FIG. 10C, the qualifying criteriacomprises a burst window 38 that gates the output of the matched filter24 as described above with reference to FIGS. 9A and 9B, so that theinterpolator 28 operates on the filtered samples 26 that represent thecenter pulse as described above. FIG. 10D shows an embodiment whereinthe qualifying criteria further comprises a coarse peak detector 40 fordetecting a coarse peak within the burst window 38, wherein the subsetof filtered samples 26 proximate the detected coarse peak are selectedfor interpolation 28. A fine peak detector 42 then processes theinterpolated samples 30 to detect a more accurate peak in the pulserepresenting the center of the servo burst.

FIG. 11 shows an example of the output of the matched filter 24 such asshown in FIG. 10A and a corresponding average timestamp 44 generatedwhen the filtered samples 26 are not interpolated (up-sampled) by theinterpolator 28, and an average timestamp 46 when the filtered samples26 are interpolated (up-sampled) by a factor of ten. This exampleillustrated how the interpolation improves the accuracy of the averagetimestamp representing the center of the corresponding burst pulse.

Any suitable control circuitry may be employed to implement the flowdiagrams in the above embodiments, such as any suitable integratedcircuit or circuits. For example, the control circuitry may beimplemented within a read channel integrated circuit, or in a componentseparate from the read channel, such as a data storage controller, orcertain operations described above may be performed by a read channeland others by a data storage controller. In one embodiment, the readchannel and data storage controller are implemented as separateintegrated circuits, and in an alternative embodiment they arefabricated into a single integrated circuit or system on a chip (SOC).In addition, the control circuitry may include a suitable preamp circuitimplemented as a separate integrated circuit, integrated into the readchannel or data storage controller circuit, or integrated into a SOC.

In one embodiment, the control circuitry comprises a microprocessorexecuting instructions, the instructions being operable to cause themicroprocessor to perform the flow diagrams described herein. Theinstructions may be stored in any computer-readable medium. In oneembodiment, they may be stored on a non-volatile semiconductor memoryexternal to the microprocessor, or integrated with the microprocessor ina SOC. In yet another embodiment, the control circuitry comprisessuitable logic circuitry, such as state machine circuitry. In someembodiments, at least some of the flow diagram blocks may be implementedusing analog circuitry (e.g., analog comparators, timers, etc.), and inother embodiments at least some of the blocks may be implemented usingdigital circuitry or a combination of analog/digital circuitry.

In addition, any suitable electronic device, such as computing devices,data server devices, media content storage devices, etc. may comprisethe storage media and/or control circuitry as described above.

The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and subcombinations are intended to fall withinthe scope of this disclosure. In addition, certain method, event orprocess blocks may be omitted in some implementations. The methods andprocesses described herein are also not limited to any particularsequence, and the blocks or states relating thereto can be performed inother sequences that are appropriate. For example, described tasks orevents may be performed in an order other than that specificallydisclosed, or multiple may be combined in a single block or state. Theexample tasks or events may be performed in serial, in parallel, or insome other manner. Tasks or events may be added to or removed from thedisclosed example embodiments. The example systems and componentsdescribed herein may be configured differently than described. Forexample, elements may be added to, removed from, or rearranged comparedto the disclosed example embodiments.

While certain example embodiments have been described, these embodimentshave been presented by way of example only, and are not intended tolimit the scope of the inventions disclosed herein. Thus, nothing in theforegoing description is intended to imply that any particular feature,characteristic, step, module, or block is necessary or indispensable.Indeed, the novel methods and systems described herein may be embodiedin a variety of other forms; furthermore, various omissions,substitutions and changes in the form of the methods and systemsdescribed herein may be made without departing from the spirit of theembodiments disclosed herein.

What is claimed is:
 1. A data storage device configured to access a magnetic media comprising a plurality of servo frames each comprising an A servo burst, a B servo burst, a C servo burst, and a D servo burst, the data storage device comprising: at least one head configured to access the magnetic media; and control circuitry configured to: read the A servo burst in a first servo frame using the head to generate a first read signal; sample the first read signal to generate first signal samples; use a first matched filter matched to the A servo burst to filter the first signal samples to generate first filtered samples within a first burst window; first update the first burst window based on the first filtered samples; process the first filtered samples within the first burst window to generate a position error signal (PES); and control a position of the head relative to the magnetic media based on the PES.
 2. The data storage device as recited in claim 1, wherein each servo burst comprises a plurality of servo stripes.
 3. The data storage device as recited in claim 1, wherein the data storage device further comprises the magnetic media, and the magnetic media includes magnetic tape.
 4. The data storage device as recited in claim 1, wherein: the magnetic media is housed in a cartridge assembly; and the data storage device further comprises a tape drive assembly configured to receive the cartridge assembly.
 5. The data storage device as recited in claim 1, wherein the first burst window estimates a center of the A servo burst in the first servo frame, and the control circuitry is further configured to: read the A servo burst in a second servo frame using the head to generate a second read signal; sample the second read signal to generate second signal samples; use the first matched filter matched to the A servo burst to filter the second signal samples to generate second filtered samples within the first updated first burst window; and second update the first burst window based on the second filtered samples.
 6. The data storage device as recited in claim 5, wherein the control circuitry is further configured to: measure an A-A burst interval representing an estimated time ta from the center of the A servo burst in the first servo frame to a center of the A servo burst in the second servo frame; and second update the first burst window based on the estimated time ta.
 7. The data storage device as recited in claim 6, wherein the control circuitry is further configured to: generate a second burst window based on the estimated time ta; read the C servo burst in the first servo frame using the head to generate a third read signal; sample the third read signal to generate third signal samples; use a second matched filter matched to the C servo burst to filter the third signal samples to generate third filtered samples within the second burst window; and process the third filtered samples to generate the PES.
 8. The data storage device as recited in claim 7, wherein the control circuitry is further configured to generate the second burst window based on a predetermined fraction of the estimated time ta.
 9. The data storage device of claim 7, wherein: the control circuitry is configured to read a second servo burst using the head, wherein the A servo burst and the B servo burst are part of a first subframe, and the C servo burst and the D servo burst are part of a second subframe; at least one of the A servo burst, the B servo burst, the C servo burst, or the D servo burst has a missing or unreadable servo stripe; and the first subframe has a first width and the second subframe has a second width equal to the first width.
 10. A data storage device configured to access a magnetic media comprising a plurality of servo frames each comprising an A servo burst, a B servo burst, a C servo burst, and a D servo burst, the data storage device comprising: at least one head configured to access the magnetic media; and control circuitry configured to: measure an estimated time ta from a center of the A servo burst in a first servo frame to a center of the A servo burst in a second servo frame; generate an A burst window for the A servo burst in a third servo frame based on the estimated time ta; read the A servo burst in a third servo frame using the head to generate a first read signal; sample the first read signal to generate first signal samples; use a first matched filter matched to the A servo burst to filter the first signal samples to generate first filtered samples within the A burst window; process the first filtered samples to generate a position error signal (PES); and control a position of the head relative to the magnetic media based on the PES.
 11. The data storage device as recited in claim 10, wherein each servo burst comprises a plurality of servo stripes.
 12. The data storage device as recited in claim 10, wherein the data storage device further comprises the magnetic media, and the magnetic media includes magnetic tape.
 13. The data storage device as recited in claim 10, wherein: the magnetic media is housed in a cartridge assembly; and the data storage device further comprises a tape drive assembly configured to receive the cartridge assembly.
 14. The data storage device as recited in claim 10, wherein the control circuitry is further configured to: generate a C burst window based on the estimated time ta; read the C servo burst in the first servo frame using the head to generate a second read signal; sample the second read signal to generate second signal samples; use a second matched filter matched to the C servo burst to filter the second signal samples to generate second filtered samples within the C burst window; and process the second filtered samples to generate the PES.
 15. The data storage device as recited in claim 14, wherein the control circuitry is further configured to generate the C burst window based on a predetermined fraction of the estimated time ta.
 16. A data storage device configured to access a magnetic media comprising a plurality of servo frames each comprising an A servo burst, a B servo burst, a C servo burst, and a D servo burst, the data storage device comprising: at least one head configured to access the magnetic media; and a means for reading the A servo burst in a first servo frame using the head to generate a first read signal; a means for sampling the first read signal to generate first signal samples; a means for using a first matched filter matched to the A servo burst to filter the first signal samples to generate first filtered samples within a first burst window; a means for first updating the first burst window based on the first filtered samples; a means for processing the first filtered samples within the first burst window to generate a position error signal (PES); and a means for controlling a position of the head relative to the magnetic media based on the PES.
 17. The data storage device as recited in claim 16, wherein the data storage device further comprises the magnetic media, and the magnetic media includes magnetic tape.
 18. The data storage device as recited in claim 16, wherein: the magnetic media is housed in a cartridge assembly; and the data storage device further comprises a tape drive assembly configured to receive the cartridge assembly.
 19. The data storage device as recited in claim 16, wherein the first burst window estimates a center of the A servo burst in the first servo frame, and the data storage device further comprises: a means for reading the A servo burst in a second servo frame using the head to generate a second read signal; a means for sampling the second read signal to generate second signal samples; a means for using the first matched filter to filter the second signal samples to generate second filtered samples within the first updated first burst window; and a means for second updating the first burst window based on the second filtered samples.
 20. The data storage device as recited in claim 19, further comprising: a means for measuring an A-A burst interval representing an estimated time ta from the center of the A servo burst in the first servo frame to a center of the A servo burst in the second servo frame; and a means for second updating the first burst window based on the estimated time ta.
 21. The data storage device as recited in claim 20, further comprising: a means for generating a second burst window based on the estimated time ta; a means for reading the C servo burst in the first servo frame using the head to generate a third read signal; a means for sampling the third read signal to generate third signal samples; a means for using a second matched filter matched to the C servo burst to filter the third signal samples to generate third filtered samples within the second burst window; and a means for processing the third filtered samples to generate the PES.
 22. The data storage device as recited in claim 21, further comprising a means for generating the second burst window based on a predetermined fraction of the estimated time ta. 